The present application relates to stationary compressors as used in power plants, refineries, pipeline compression of natural gas, and other installations where gasses are compressed for industrial purposes, and more particularly to the in-service monitoring and analysis, such as electronic analysis, of the condition and performance of such compressors, and most particularly to suction and discharge valves that are adapted and configured for facilitating in-service monitoring.
An industrial reciprocating gas compressor is a positive-displacement machine wherein the gas to be compressed is trapped in an enclosed space and then squeezed into a small volume by the action of a piston moving inside a cylinder. The gas is compressed to a pressure sufficient to overcome the discharge pressure plus the spring tension holding the discharge valve closed, at which time the discharge valve opens and allows the compressed gas to leave the cylinder. Because of the nature of the reciprocating piston, compression ceases at the limits of its stroke, the discharge valve again closes due to the action of the springs on the valve, the piston reverses direction, and the small amount of gas remaining in the cylinder expands, increasing in volume and decreasing in pressure. When the inlet pressure is higher than the pressure inside the cylinder plus the spring tension holding the suction valve closed, the suction valve then opens, allowing gas to flow into the cylinder. At the opposite limit of the piston stroke, the suction valve closes due to the springs acting on the valve, the piston again reverses direction, and the compression cycle begins anew.
The rate of pressure rise with respect to piston position in the cylinder, the exact moment of valve actuation, actual pressures attained, and other information concerning the compression, discharge, re-expansion, and inlet events taking place in the cylinder have long been recognized to be of value to engineers in assessing the operating condition of compressors. The first instrument used to record such information was a mechanical device which comprised a stylus attached to a pressure indicator and a rotating drum which was activated in proportion to the movement of the piston by a string attached to the crosshead of the compressor. The instrument was attached to the cylinder with a three-way valve, and sensed pressures inside the cylinder via passages (indicator ports) drilled during manufacture of the compressor.
The state of the analyzing art advanced during the 1960s with the introduction of the BETA 100, an oscilloscope device that utilized pressure transducers to sense pressure through indicator ports, and determined piston location from the angle of the crankshaft of the compressor. Further refinements of such electronic analyzers have been based on the principles of the early devices, and now include displays of pressure/volume or pressure/time, automatic calculation of horsepower consumed by the cylinder, and volumetric efficiency of the cylinder, as well as analysis of each valve event. Data from vibration transducers and ultrasound detectors (for analyzing the behavior of individual valves) are routinely superimposed on the pressure-volume trace to pinpoint operational problems and to determine the need for maintenance. Data from the analyzer may be sent to a personal computers for the automatic generation of reports. Significant savings in operational expenses and maintenance costs are attainable if the information is analyzed at routine intervals.
There was a time gap between the use of the drum-and-stylus instruments and the modem electronic instruments, however, and during that time gap manufacturers stopped providing indicator ports in cylinders and usually did not list indicator ports as an option when ordering a new machine. As a result, many compressors currently in operation do not have indicator ports and therefore cannot be analyzed properly.
Detailed description of a more or less contemporary monitoring system for reciprocating piston machines, including the use of pressure transducers, is given by Wiggins in U.S. Pat. No. 4,456,963, the disclosure of which is herein incorporated by reference. Other references to the use of pressure monitoring are given by Rice in U.S. Pat. No. 4,111,041 and Abnett et al in U.S. Pat. No. 4,325,128, the disclosures of which are incorporated herein by reference. However, none of these references utilize pressure transducers to sense the cylinder pressure through the center bolt of a suction or discharge valve or disclose indicator ports incorporated within the valve body, as disclosed herein.
Installation of indicator ports after the manufacture of the compressor traditionally involves the complete disassembly of the compressor and tedious machine shop work to locate and drill the indicator ports. During this process, the compressor must remain out of service for extended periods of time with lost production costs accumulating. Often, the cylinder casting does not have provisions for adding an indicator port, and installing one may entail penetration and sealing the water jacket surrounding the cylinder. Without indicator ports, much of the intelligence necessary for analysis is lost. Thus, there is clearly a need for a simple and effective system and method to equip compressors that have not been manufactured with indicator ports with means for monitoring compressor cylinder condition and performance. Such systems and methods should provide a means for monitoring compressor performance without significantly increasing the space required to house the compressor and at the same time should provide adequate protection for the sensitive monitoring equipment.
This present application discloses an improved valve configuration such that an indicator port is incorporated directly within either a suction or a discharge type valve thereby allowing a sensing device to be mounted directly to the valve or within the valve body. It is generally understood that suction and discharge valves used in certain applications such as compressors, can be interchangeable and therefore, this application is directed to both of these types of compressor valves and the disclosure herein is applicable to both suction and discharge valves.
An object of the present application is to provide a simple and effective system and method to equip compressors with means for monitoring compressor cylinder condition and performance. Yet another object of the present application is to provide a location within the valve for the sensing device that inherently protects it from damage, enabling the device to function properly and increasing its expected service life.
Still yet another object of the present application is to simplify the installation of the sensing device by allowing it to be provided as part of a complete assembly. The sensing device can be provided already installed within a replacement valve for an existing compressor, or it can be provided as part of a valve assembly to be installed in a new compressor.
In accordance with these and further objects, one aspect of the present application includes a valve for sensing at least one condition within a compressor comprising a compressor cylinder, a piston, at least one discharge valve, and at least one suction valve. The valve includes a valve guard defining outlet flow ports and having a central aperture being disposed therein. The valve further includes a valve seat defining inlet flow ports and having a central aperture. An elongated structure such as an elongated stud is operatively engaged in the central aperture of the valve guard and valve seat and defines a central axis for the valve. The elongated structure has a hollow core which creates an indicator port extending from the interior of the compressor cylinder to an exterior terminus at the exterior of the valve. Additionally, a sensing device is operatively connected to the exterior terminus of the indicator port. The sensing device may comprises a pressure transducer for sensing pressure in the interior of the compressor cylinder. Alternatively, the sensing device may comprise a means for sensing the temperature, vibration, gas flow or the position of the piston within the compressor.
The present application is also directed to a valve for sensing at least one condition within a compressor comprising a compressor cylinder, a piston, at least one discharge valve, and at least one suction valve. The valve includes a valve seat defining inlet flow ports through which gas enters the valve and a valve guard defining outlet flow ports through which the gas exits the valve. A hollow area is operatively positioned in the valve guard or valve seat which is adapted and configured for housing a sensing device.
The valve further includes a bore in the valve seat for facilitating electrical communication with the sensing device. Electrical signal communicating structure, such as wiring, extends through this bore and connect the sensing device to a monitoring device. The monitoring device translates the signal received from the sensing device to data which can be interpreted by an operator, engineers or maintenance personnel in order to evaluate the condition and performance of the compressor. Preferably, the sensing device is a pressure transducer for sensing pressure in the interior of the compressor cylinder. Alternatively, the sensing device can be a means for sensing temperature or other condition within the interior of the compressor cylinder.
The present application is also directed to a system for sensing at least one condition within a compressor comprising a compressor cylinder, a piston, at least one discharge valve, and at least one suction valve. The valve includes a valve guard defining outlet flow ports, a valve seat defining inlet flow ports, a hollow area operatively positioned in the valve guard or valve seat, a sensing device operatively positioned within the hollow area, and a monitoring device located exterior to the valve in communication with the sensing device.
Other objects, features and advantages of the present application will be apparent from the following description, the accompanying drawings and the appended claims.